Patients' self-care is a critical element in the control of many chronic illnesses, including diabetes, yet depression may lead to poor self-care behaviors. To date there are no large, population-based, longitudinal studies examining the relationship between depression and self-care in diabetic patients. The proposed study extends previous work on self-monitoring of blood glucose (SMBG) and medication compliance among diabetic patients and will determine the association between depression and objectively determined rates of self-care (including SMBG and regularity of drug therapy) in patients newly treated for diabetes in a managed care organization. Using these measures, we will address whether and to what extent diabetic patients who use anti-depressant medications initiate and maintain self-care regimens compared with diabetic patients who do not use anti-depressant medications. We will define a rolling cohort of all newly treated diabetic patients in the years 1991 through 1995 who have been given at least one prescription for an anti-depressant medication during the period of three months prior to and three months after initiation of diabetes medication treatment. We will include all patients 18 years and older who are first treated for diabetes after at least six months of continuous enrollment who were also continuously enrolled for at least three months after initiation of medication treatment. Access to computerized medical records, inpatient claims, lab results, and pharmacy data at HVMA will allow us to create reliable, objective measures of self-monitoring (e.g., home glucose monitor test strip use) and regularity of drug use (e.g., measured using gaps in drug refills). The use of patient-level longitudinal methods (specifically survival analysis) will allow us to control for both patient-level and time-dependent covariates that might confound study results. We will also stratify analyses by type of drug therapy (i.e., insulin only, combination insulin/oral drug therapy, or oral hypoglycemic only) to control for severity of illness.